1. Field of the Invention
The present invention relates to a reflector and a liquid crystal display panel, and particularly to a thin reflector and a liquid crystal display panel causing little deterioration of reflectance over a long period of time.
2. Description of the Related Art
A reflective liquid crystal display device utilizes sunlight, illuminating light of a front light or the like as a light source, and is frequently used for a personal digital assistant and the like required to have low power consumption. A transflective liquid crystal display device as another example of liquid crystal display devices is operated in a transmissive mode with a back light lighted in an environment where external light cannot be sufficiently obtained, and operated in a reflective mode with the back light not lighted when external light can be sufficiently obtained. The transflective liquid crystal display device is frequently used for portable electronic apparatuses such as a cellular phone, a notebook-size personal computer, and the like.
A conventional reflective liquid crystal display device will be described with reference to the drawings. As shown in FIG. 18, a conventional liquid crystal display device 101 roughly comprises a liquid crystal display panel 120, and a front light 110 disposed on the observer side of the liquid crystal display panel 120.
The liquid crystal display panel 120 roughly comprises a first substrate (a substrate) 121 and a second substrate (another substrate) 122 which are opposed to each other with a liquid crystal layer 123 provided therebetween and which are combined together with a sealing material 124. Each of the first substrate 121 and the second substrate 122 is a transparent substrate such as a glass substrate or the like. Also, display circuits 126 and 127 are provided on the liquid crystal layer sides (inner sides) of the substrates 121 and 122, respectively. Although the display circuits 126 and 127 are not shown in particularity in the drawing, the display circuits include an electrode layer comprising a transparent conductive film or the like for driving the liquid crystal layer 123, an alignment film for controlling the orientation of the liquid crystal layer 123, etc. In a color display, the display circuits 126 and 127 may include a color filter.
Also, a reflector 130 is attached to the outer side of the second substrate 122. The reflector 130 comprises a reflecting layer 128 made of a resist resin, a polycarbonate resin, or the like, a planarizing layer 129 laminated on the reflecting layer 128, and an adhesive layer 131 laminated on the planarizing layer 129 and put into contact with the second substrate 122. Furthermore, a plurality of recesses 128b is provided on the surface of the reflecting layer 128, and a highly reflective film 128a made of Al is formed on the recesses 128b. The planarizing layer 129 is laminated in contact with the highly reflective film 128a. The shape of recesses 128b is reflected in the highly reflective film 128a. 
The recesses 128b of the reflecting layer 128 are formed by, for example, a so-called heat embossing method (embossing method) in which first, an electroforming pattern having an irregular surface is prepared, and a polycarbonate thin plate used as the reflecting layer is pressed on the heated surface of the electroforming pattern to transfer the irregularities of the surface to the polycarbonate thin plate by embossing.
The front light 110 is disposed on the outside (the observer side) of the first substrate 121 of the liquid crystal display panel 120. The front light 110 comprises a transparent light guide plate 112 made of, for example, an acrylic resin or the like, and a light source 113 comprising a cold-cathode tube provided on the side end 112a. The bottom (facing the liquid crystal display panel 120) of the light guide plate 112 functions as a smooth emission plane 112b through which light is emitted. The opposite surface (the top of the light guide plate 112) of the light guide plate 112 to the emission plane 112b functions as a prism plane 112c having a plurality of wedge grooves formed in stripes with a predetermined pitch for changing the direction of light propagated in the light guide plate 112.
In the conventional reflective liquid crystal display device 101, incident light such as the illuminating light from the front light 110 or sunlight is transmitted through the liquid crystal layer 123 of the liquid crystal display panel 120, reflected by the highly reflective film 128a formed on the reflecting layer 128, again transmitted through the liquid crystal layer 123 and then emitted as emitted light to the observer side. A construction similar to the liquid crystal display device 101 is disclosed in a prior document, for example, Japanese Unexamined Patent Application Publication No. 2002-22913.
Although the conventional liquid crystal display device 101 uses the reflecting layer 128 made of polycarbonate as a base material of the highly reflective film 128a in some cases, the polycarbonate has relatively high moisture absorption and thus has high permeability to moisture. Therefore, atmospheric moisture penetrates into the reflecting layer 128 and reaches the highly reflecting Al film 128a to convert Al to aluminum hydroxide or aluminum oxide with permeated moisture. When Al is converted to aluminum hydroxide or aluminum oxide, the highly reflective film 128a becomes translucent to cause the problem of significantly decreasing the reflectance of the reflector 130.
In the conventional liquid crystal display device 101, the surface of the reflecting layer 128 is formed by the heat embossing method, and thus the thickness of the reflecting layer 128 must be increased to some extent to increase strength. Therefore, the thickness of the reflector 130 is increased to cause the problem of failing to thin the liquid crystal display device 101.
For example, the liquid crystal display device 101 is used as an on-vehicle device, the liquid crystal display device 101 is placed in an environment of high temperature. In this case, considering the linear expansion coefficient of each component member, the linear expansion coefficient of the reflecting layer 128 (polycarbonate) is higher than that of the second substrate 122 (glass), and thus the amount of expansion of the reflecting layer 128 at high temperature becomes large. As a result, as shown in FIG. 29, a part of the reflector 130 is possibly separated from the second substrate 122 since a lift force due to expansion of the reflecting layer 128 exceeds the adhesive force of the adhesive layer 131 to the second substrate 122. Such lifting might significantly impair the appearance of a display device.